[SAO PAULO] The Zika virus may not have acted alone to cause an unusual cluster of microcephaly cases in northeastern Brazil, according to a study that evaluated factors related to the distribution pattern of the disease across the country.

Researchers have estimated that the Zika virus reached Brazil in 2013, and that it soon spread through the country, triggering outbreaks of infections until mid-2016.

One of the consequences of this epidemic was the increase of microcephaly cases, a birth defect where the baby's head and brain is abnormally small.

However, although Zika infections have been reported throughout Brazil, cases of congenital microcephaly have been concentrated in the northeastern part of the country — a pattern that was believed to be linked to the arrival of the virus through that region.

Setting out to understand other factors that may be associated with this pattern, a team of Brazilian researchers analysed epidemiological data from 2014 to 2016, which were gathered by local branches of the Brazilian Ministry of Health.

According to their paper, published in PloS One, Brazil registered an average of 156 cases of microcephaly per year between 2010 and 2014 — but by the end of 2015, the number had risen 20-fold.

Pernambuco was the first state to report an unusual number of microcephaly cases in newborns, with 10 times more reports than the average for the entire country in the previous five years.

The number of reported cases continued to increase. Out of 10,867 registered between November 2015 and the end of 2016, 7,023 were located in the Northeast — and of the 10 states with the highest number of microcephaly cases related to Zika infection, nine were from the Northeast.

According to data gathered by the Brazilian Institute of Geography and Statistics, this region also has the country’s highest poverty rate, lowest socioeconomic status, and poorest environmental management.

Together, these factors are expected to increase the proliferation of Aedes mosquitoes, which in addition to Zika also transmit yellow fever, dengue and chikungunya viruses.

The study found a correlation between the distribution of chikungunya infection and congenital microcephaly in the region, which the authors say may indicate that previous arbovirus infections or co-infection with chikungunya can increase the severity of Zika infections.

They also speculate that malnutrition and overall poor health associated with poverty could compromise immunity, as well as the body’s response to infection and the clinical progression of the disease.

“The findings suggest that cases of microcephaly due to Zika may be associated with a combination of epidemiological, environmental and socioeconomic factors,” says Jamille Dombrowski, form the Institute of Biomedical Sciences of the University of Sao Paulo, and one of the authors of the study.

According to Jean Pierre Schatzmann Peron, also from the Institute of Biomedical Sciences of the University of Sao Paulo, the study makes a comprehensive and integrative analysis of the factors that may have contributed to the epidemic of microcephaly in Brazil.

He says the study is significant because it builds a socioeconomic profile of the Zika epidemic in the country, which can inform government policies to prevent new cases and help those already affected by the virus.

“The results must be taken seriously to improve public policies on sanitation and health,” he concluded. The authors recommend measures such as raising awareness and genomic epidemiology studies to better understand the impact of the virus.